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ILS vs LPV


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 let’s say the weather is right at 200 1/2 or maybe even a little bit lower and you are really running low on fuel. We know and ILS will give guidance all the way down to the runway for the most part. CAT 2 and 3 Approach certified facilities certainly will,  and cat 1 facilities will provide guidance although it’s not really tested in that area. But still, the needles work...But are we sure that a LPV does the same thing ? In other words what do you do whenever you get to DA and the needles disappear on the LPV, what do you do then?  Admittedly I haven’t tried to fly a GTN750 below DA but IIRC it suspends and gives a “missed approach point reached” message. IDK if the needles are removed from the Sandel  

I’m not advocating busting minimums anything like that. I’m just saying that if you’re really there running low on fuel and you really have to make it in and you may have to continue below MDA to the runway because it’s safer option than going around, are you  sure that an LPV approach gives  guidance below DA? 

Edited by jetdriven
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1 hour ago, jetdriven said:

 let’s say the weather is right at 200 1/2 or maybe even a little bit lower and you are really running low on fuel. We know and ILS will give guidance all the way down to the runway for the most part. CAT 2 and 3 Approach certified facilities certainly will,  and cat 1 facilities will provide guidance although it’s not really tested in that area. But still, the needles work...But are we sure that a LPV does the same thing ? In other words what do you do whenever you get to DA and the needles disappear on the LPV, what do you do then?  Admittedly I haven’t tried to fly a GTN750 below DA but IIRC it suspends and gives a “missed approach point reached” message. IDK if the needles are removed from the Sandel  

I’m not advocating busting minimums anything like that. I’m just saying that if you’re really there running low on fuel and you really have to make it in and you may have to continue below MDA to the runway because it’s safer option than going around, are you  sure that an LPV approach gives  guidance below DA? 

In the 3 different platforms I have flown with LPV (Beech 400, PC-12 and my Mooney) you continue to be provided guidance, lateral and vertical, inside/below DA.  It just does not automatically sequence to the missed approach unless you un-suspend.  At airfields without VASI or PAPI, I continue to cross check the GP to prevent a duck under landing.

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4 hours ago, m20c1967 said:

what airport has same mins for ils and rnav ?

 

A lot of the ones I've looked at. It would be interesting to get some real numbers but my impression is the exact opposite - that in most cases colocated LPV and ILS minimums are identical. I just double-checked 4 airports in my general area - one Class C (I chose one approach there) and the rest nontowered -  and that was the case for all of them. Checked another two where I used to live. Same thing.

i guess it's about looking at the approach and seeing which appears to give better options for the specific flight.

Edited by midlifeflyer
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1 hour ago, jetdriven said:

 let’s say the weather is right at 200 1/2 or maybe even a little bit lower and you are really running low on fuel. We know and ILS will give guidance all the way down to the runway for the most part. CAT 2 and 3 Approach certified facilities certainly will,  and cat 1 facilities will provide guidance although it’s not really tested in that area. But still, the needles work...But are we sure that a LPV does the same thing ? In other words what do you do whenever you get to DA and the needles disappear on the LPV, what do you do then?  Admittedly I haven’t tried to fly a GTN750 below DA but IIRC it suspends and gives a “missed approach point reached” message. IDK if the needles are removed from the Sandel  

I’m not advocating busting minimums anything like that. I’m just saying that if you’re really there running low on fuel and you really have to make it in and you may have to continue below MDA to the runway because it’s safer option than going around, are you  sure that an LPV approach gives  guidance below DA? 

Sounds like an experiment needs to be run. Easy enough to do, setup a camera, fly an LPV and land instead of doing a missed. If I ever get my brakes fixed, I'll try it. 

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4 hours ago, jetdriven said:

I’m not advocating busting minimums anything like that. I’m just saying that if you’re really there running low on fuel and you really have to make it in and you may have to continue below MDA to the runway because it’s safer option than going around, are you  sure that an LPV approach gives  guidance below DA? 

2 hours ago, Marauder said:

Sounds like an experiment needs to be run. Easy enough to do, setup a camera, fly an LPV and land instead of doing a missed. If I ever get my brakes fixed, I'll try it. 

It sounds more like a the beginning of an NTSB report discussing the chain of events which lead to the accident.

Here's what the GTN looks like after crossing DA on the GPS 5R at RDU (one of those with a 200' DA). "Suspend" means suspending automatic sequencing to the next waypoint. It does not mean suspending course guidance. As you can see here, the CDI is still centered on the FAC; there's just no magenta line to the first missed approach waypoint. 

Of course, on the opposite end of the approach, with LPV you can capture the glideslope much further out and not have to worry about false gideslopes.

image.png.88a41ed3bff065b251ec01bb5494cc07.png

 

 

Edited by midlifeflyer
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It sounds more like a the beginning of an NTSB report discussing the chain of events which lead to the accident.
Here's what the GTN looks like after crossing DA on the GPS 5R at RDU (one of those with a 200' DA). "Suspend" means suspending automatic sequencing to the next waypoint. It does not mean suspending course guidance. As you can see here, the CDI is still centered on the FAC; there's just no magenta line to the first missed approach waypoint. 
Of course, on the opposite end of the approach, with LPV you can capture the glideslope much further out and not have to worry about false gideslopes.
image.png.88a41ed3bff065b251ec01bb5494cc07.png
 
 


I’m not sure where you got the idea that either of us were advocating doing this in real conditions and with our eyes fixated on the needles. Setting up a GoPro aimed at the panel is an easy and safe way to watch what the needles do during the sub-DA area.

I am confident the lateral guidance stays active and accurate. I just don’t know what the vertical guidance does.


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19 minutes ago, Marauder said:

 


I’m not sure where you got the idea that either of us were advocating doing this in real conditions and with our eyes fixated on the needles. Setting up a GoPro aimed at the panel is an easy and safe way to watch what the needles do during the sub-DA area.

I am confident the lateral guidance stays active and accurate. I just don’t know what the vertical guidance does.


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I didn't get the idea you were advocating doing it in real conditions. I don't have an issue with finding out what the GS does as an academic exercise. Knowledge is always a good thing.

OTOH, I've seen two primary arguments in this thread  why some feel an ILS is intrinsically "better"

One was that minimums "are" lower. That's not generally true and if it is, it's just an argument for looking at an airport's  approach alternatives.

The second is a scenario in which one would not "advocate" but "might" find the need to follow the approach below minimums and all the way to touchdown. Sorry, but low on fuel and heading to an airport where the weather is at or below minimums because you have to get there  does read like a common accident chain in which missionitis combines with poor planning and poor enroute decision making.

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A bit off topic, but here is the basic thought process I went through concerning weather when I was flying the DC9.  It helped me decide if I wanted to ask the dispatcher for more fuel.  I do not want to be that guy who has to bust minimums because I didn't bring enough fuel.  Granted the chart is for whether or not I would let the dispatcher use an exemption to avoid giving me an alternate, but the same logic could apply for deciding if you need more fuel.

 

Fuel Decision.jpg

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2 hours ago, Marauder said:


I am confident the lateral guidance stays active and accurate. I just don’t know what the vertical guidance does.
 

 

Simulators aren't perfect, but I ran an LPV approach in Garmin's G1000 simulator. You can see from this screen capture that we are well below minimums (just passed over the runway numbers) and the glidepath is still annunciating. A few seconds later, after going beyond where  the glidepath intersects the runway, the annunciation changed to "no glidepath," which makes sense.

Assuming this is an accurate rendition of what the G1000 does, I'd expect the same behavior from any WAAS-enabled approach certified GPS. It will e interesting to see what you test shows.

 

image.png.2ebac481d399060d313f8a41d649e064.png

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7 hours ago, jetdriven said:

 let’s say the weather is right at 200 1/2 or maybe even a little bit lower and you are really running low on fuel. We know and ILS will give guidance all the way down to the runway for the most part. CAT 2 and 3 Approach certified facilities certainly will,  and cat 1 facilities will provide guidance although it’s not really tested in that area. But still, the needles work...But are we sure that a LPV does the same thing ? In other words what do you do whenever you get to DA and the needles disappear on the LPV, what do you do then?  Admittedly I haven’t tried to fly a GTN750 below DA but IIRC it suspends and gives a “missed approach point reached” message. IDK if the needles are removed from the Sandel  

I’m not advocating busting minimums anything like that. I’m just saying that if you’re really there running low on fuel and you really have to make it in and you may have to continue below MDA to the runway because it’s safer option than going around, are you  sure that an LPV approach gives  guidance below DA? 

I don't know this for sure, but since regulations specify you can follow the guidance for any approach down to 100' AGL if you have the approach information (lighting) in view, I have to imagine that ALL authorized approach equipment are TSO'd to provide guidance at least that low.  I assume this is buried somewhere in TSO C-145c or C-146c?

Incidentally, I never realized this, but am I correct in my reading of FAR 91.175 that you can descend to 100' AGL with the approach lights from ANY type of approach (precision OR non-precision)??

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I didn't get the idea you were advocating doing it in real conditions. I don't have an issue with finding out what the GS does as an academic exercise. Knowledge is always a good thing.
OTOH, I've seen two primary arguments in this thread  why some feel an ILS is intrinsically "better"
One was that minimums "are" lower. That's not generally true and if it is, it's just an argument for looking at an airport's  approach alternatives.
The second is a scenario in which one would not "advocate" but "might" find the need to follow the approach below minimums and all the way to touchdown. Sorry, but low on fuel and heading to an airport where the weather is at or below minimums because you have to get there  does read like a common accident chain in which missionitis combines with poor planning and poor enroute decision making.


What do you think of this guy’s flight?

https://youtu.be/OUUxjSmXcpk


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2 hours ago, jaylw314 said:

I don't know this for sure, but since regulations specify you can follow the guidance for any approach down to 100' AGL if you have the approach information (lighting) in view, I have to imagine that ALL authorized approach equipment are TSO'd to provide guidance at least that low.  I assume this is buried somewhere in TSO C-145c or C-146c?

Incidentally, I never realized this, but am I correct in my reading of FAR 91.175 that you can descend to 100' AGL with the approach lights from ANY type of approach (precision OR non-precision)??

You are correct in your reading that 91.175(c) applies to both precision and nonprecision approaches. But you might want to read Jeff Van West's discussion of the rule in IFR Magazine - it's one of those which are publicly readable without a subscription.

I'm not sure I agree completely with the article, but I definitely see his point about there  being two conditions which must be met  to take advantage of it: flight visibility  continuously above minimums for the approach and the ability to land using normal maneuvers. That probably limits its practicality for nonprecision approaches.

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Exactly what I think of most all of Jerry's IFR  flights. 


I have been watching his videos over the past few months. One thing that isn’t noted in this video is that he has literally just installed this panel. And I mean literally. His “first flight” video was posted on December 9th. I don’t know about the rest of you who have done glass conversions, but it took me a number of hours to get used to the functionality.

I certainly wouldn’t be shooting approaches for real with those minimums.


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6 hours ago, Marauder said:

What do you think of this guy’s flight? emoji6.png

https://youtu.be/OUUxjSmXcpk


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The nitpicker in me points out when he crosses the last RAIL flasher at 1400', there is no runway in sight so he clearly has less than 1400' of flight visibility.  The minimum RVR for OAK ILS 28R is 2400.  While the camera might not be able to see the runway through the fog as well as the human eye, he clearly calls out "airport in sight" when he is well within the 1000' three-bar light and when the threshold becomes visible on the camera.  In fact, with the MALSR, you'd need to see the threshold just as you crossed over the first RAIL flasher (which we never saw).  And thanks to @midlifeflyer for reminding me, you can't go below 100' AGL with the approach lights only since the MALSR does not have any red bars.

Put together, I'd say that's clearly below the minimums allowed.

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5 minutes ago, midlifeflyer said:

You should have seen some of the ones he's removed because they were so awful. There's one in which he exits the clouds in an unusual attitude.

:o  I noticed in one of his replies, he claimed he was about to say "got the runway in sight" at DA, which seems doubtful.  But then later you hear him announce "got the airport in sight" right when the threshold appears on the camera, so one wonders what he meant.

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